Field of the Invention
The present invention concerns devices and techniques for avoiding collisions in the environment of a system having a heavy, movable component, and personnel and/or objects that are present in the environment of the system while that component may be moving. In particular; the present invention concerns avoiding such collisions between persons, including operating personnel and patients, as well as other objects that are present in an examination room in which a medical examination or procedure is being implemented using a medical apparatus that has at least one such heavy, movable component, such as a robotically-operated x-ray imaging system.
Description of the Prior Art
Medical diagnosis and intervention systems of the type used in angiography, cardiology, neurology and hybrid procedures often have relatively heavy components that are mounted, such as on a C-arm, for movement relative to a patient, so as to be positioned relative to the patient for a particular purpose, such as for obtaining a medical image of the patient. For conventional two-dimensional imaging, the components of the imaging apparatus can be positioned by respective motor drives in a flexible manner around the patient lying on a patient bed or patient table. For 3D imaging, these components can be driven automatically or semi-automatically around the patient, in order to acquire a larger number of individual images that are necessary for the 3D image reconstruction.
In addition to x-ray mounting arrangements, such as floor-mounting and ceiling-mounted brackets with articulated arms, it has become increasingly popular to employ robots of the type used for industrial purposes in order to position a C-arm, on which components such as an x-ray source and a radiation detector are mounted, relative to the patient. These types of robotically-operated imaging systems allow for high-precision positioning and kinematics. Such robots typically exhibit multi-axis kinematics, and the increase in the degrees of freedom of movement of the overall system increase the requirements for safety in the environment in which such systems are operated. Particularly in environments wherein human/robot collaboration exists (i.e., humans and the robot are both moving in the same room and with respect to a common focus, namely the patient), the possibility of one of the moving, heavy components coming into contact with a human, either the patient or attending personnel, exists, and steps must be taken to avoid injuries due to such potential collisions.
There is also a risk that the moving component may collide with an object within its movement range, thereby damaging the component or the object, or both.
In workspaces of the type described above, it is generally not possible to install protective devices that would physically separate humans in the environment from a collision with a component moved by the robot. Therefore, other protective measures are known in order to detect the possibility of a collision occurring, and to continually minimize this possibility via the robot controller, such as by reducing the speed of movement when the components moved by the robot controller are in proximity to the patient table.
Since contact between personnel/objects and moving objects can occur anywhere in an operating room environment and at any time, a risk of collision remains, despite the use of known collision-detection techniques. In order to minimize this risk as much as possible, it would be desirable to have a collision-detection technology in place that is effective for avoiding collision between personnel/objects and all portions of all surfaces of components or assemblies that, when moving, would present a risk of injury to such personnel. This requires a sensor technology that is “surface-covering,” meaning that sensing capability is provided over the entire surface of any component or assembly that presents a risk of injury due to a collision.
In addition to the requirements imposed by the industry standard for robots (DIN EN ISO 10218, Parts 1 and 2, Medicine Standard IEC 60601-1, 3rd Edition, namely the “first fault safety” described therein), such as sensor technology must take into account the technically feasible solutions and be capable of differentiation among various injury classes (for example, according to the AIS 98 Code, Abbreviated Injury Scale).
Current angiography systems, for example, typically have different integrated collision protection mechanisms that can include stored software models, electronic permission buttons (DMG, Dead Man Grip) and additional protective measures. Examples of such known collision-detection mechanisms and measures are as follows.
Collisions at resiliently-mounted housing parts of the C-arm radiation source/detector can be detected by the triggering of electronic buttons that are situated on those components. Such an approach is described in U.S. Pat. No. 6,550,964.
Electrical signal-generating, pressure-sensitive bumpers can be attached to the profile of the C-arm, which function as resistive switching elements. These types of bumpers emit a signal when a relatively strong deformation of the pressure-sensitive bumper occurs, and this signal is supplied to a control circuit for analysis and evaluation for collision detection and avoidance. Such a pressure-sensitive bumper is described in German Utility Model DE 9403972 U1.
Another known approach is described in U.S. Pat. No. 5,570,770 wherein the motor current supplied to actuators of drive motors, which move various components in an x-ray examination room, is monitored in order to detect that a collision has taken place.
In general, it is also known to locate acceleration sensors and/or force sensors, such as strain gauges, magnetic field sensors, etc., at appropriate locations on respective components in order to provide signals that can be used for collision detection.
A disadvantage that all of these known approaches have in common is that they are difficult to integrate into the covering of a surface, particularly complexly-shaped surfaces of parts of a medical apparatus, in a cost-effective manner, while still maintaining reliable collision detection. For example, the aforementioned pressure-sensitive bumpers, which emit an electrical signal when strongly deformed, can be used individually and locally only to a limited extent, due to the geometry of such bumpers. Moreover, such known pressure-sensitive bumpers provide the most reliable emission of a signal when the force (impact) applied thereto occurs substantially perpendicularly to the pressure-sensitive surface of the bumper. Impact angles that are greater than 45° can lead to an erroneous response. Moreover, such bumpers usually are not able to detect collisions that occur within a few millimeters from the edges of the bumper. When such bumpers have been attempted to be used to provide coverage over a relatively large area, a large number of individual pressure-sensitive bumpers are connected together on the surface of the component in question, and are covered with foam, and the surface is then subsequently finished with a highly flexible lacquer. The lacquered foam coating is very expensive, and is subject to being damaged by sharp articles.
With regard to the approach involving resiliently mounted housing parts, such housing parts must be able to function in any spatial support/orientation, and in response to any desired movement acceleration. This means that such parts can have only a predetermined maximum weight, otherwise the restoring force on the housing thereof would be too large in order to trigger a detection in the event of a collision. Moreover, such buttons each detect movement along a particular direction. Because collision with such a housing can occur from many different directions, detection must be ensured in all directions, and this can be realized only by using a very complex and mechanically delicate and expensive configuration.
Moreover, separation lines, such as produced by edges and grooves, must be provided in order to achieve this movement detection, and sterilization and hygienic problems can result from the presence of such crevices in a medical environment.
Membranes made of polyvinylidene fluoride (PVDF) are known for many different purposes in many different fields. PVDF membranes are known, for example, for use as pressure-sensors when stretched over a surface with an underlying clearance beneath the membrane, in the manner of a drumhead stretched over the surface. Such a clearance beneath the PVDF membrane is necessary in such arrangements in order to permit the membrane to be deformed by a sufficient amount so as to detect and measure the applied pressure. PVDF membranes are also known for use in a manner similar to stream gauges. Known problems associated with PVDF membranes designs are the implementation of large-area elements, applications with large force impacts, and exposure to sharp articles. When PVDF membranes have been used in the context of a pressure-based design, they typically exhibit only a small dynamic range, and this range is strongly dependent on the supporting structure for the membrane, because only a mechanical change of the film in terms of its thickness can be detected in order to provide the relevant signal.
PVDF is a semi-crystalline plastic that is known to be piezoelectric, i.e., it can produce an electrical signal when subjected to a deformation. Such material is known for use as an acoustic sensor, such as in a microphone, as well as an acoustic actuator, such as in a speaker. PVDF membranes are also known for use in certain controlled electromechanical systems, such as in force-regulated piezo-servo motors. In medical technology, ultrasound heads are known that make use of PVDF film to not only emit the ultrasound signal, but also to receive the reflected signal.